Abstract
Congenital hallux varus had been a well-described condition for many years before acquired hallux varus as a condition arising from bunion correction was not described until 1935. In that year, McBride discussed this potential problem when describing this as a potential problem from his described technique, identifying possible mechanisms to prevent the disorder from occurring. Authors such as Joplin and Kelikian echoed the concept in the early 1960's, spawning a series of corrective procedures. Miller brought this to common practice in 1975, describing the tendon imbalance seen across the precarious 1st MTP joint.
The first metatarsophalangeal joint moves in the sagittal plane, dorsiflexion and plantarflexion only. Four intrinsic muscles stabilize the digit, with the abductor and adductor hallucis taking the lion share of this function. The abductor tendon actually functions primarily as a plantarflexor of the first metatarsophalangeal joint 83% of the time (Thompson) due to its primary plantar location. This fact, in combination with the pronation generally seen in severe bunion deformities, contributes to acquired hallux varus following bunion correction. Besides the obvious cause of over-correction of the metatarsal osteotomy creating hallux varus, imbalance of the tendon complex post-operatively can create an equally catastrophic circumstance. Hawkins demonstrated that severing the adductor tendon complex (the conjoined tendon) will not product hallux varus when the hallux is not rotated. However, in more severe hallux valgus, pronation of the hallux may be proportional to the deformity of the hallux itself. This rotational deformity places the insertions of the abductor (and medial insertion of the flexor brevis) more plantarward and lateral, increasing the valgus deformity. If the entire conjoined tendon is sectioned and the internal rotation deformity corrected the insertion of the contracted abductor moves medially, pulling the toe into varus. If the center of the base of the proximal phalanx is brought beyond the mid-point of the first metatarsal head, the extensor hallucis longus will bowstring, pulling the great toe into varus while creating a hallux flexus deformity. Finally, if the lesser toes are in varus and not corrected, this deforming force will create hallux varus following bunion correction with a lateral release. The message is clear: not all patients require a lateral release, and, if done, should be done with caution.
Once present, correction can be difficult. Tendon transfers utilizing the extensor hallucis longus (Johnson) or extensor hallucis brevis (Myerson) only have beneficial effects in non-arthritic, mobile first metatarsophalangeal joints. In addition, if metatarsal deformity is not corrected, the deformity will recur. Thus, in many circumstances, arthrodesis of the first metatarsophalangeal joint becomes the treatment of choice, and is commensurate with a disappointed patient who underwent a primary bunion correction and was left with a fused great toe.
This lecture will explore the above mechanism and salvage situations, in hopes of eliminating this unwelcomed outcome from your practice.
